Many machines use transmissions to couple the output of a prime mover or power source, for example, an internal combustion engine, to a driven element or device such as wheels or a work implement. Traditional transmissions typically included one or more fixed, selectably engageable gear ratios that could increase or decrease the speed of the prime mover and, usually in an inverse relationship, the torque. Specific gear ratios often correspond to discrete and known speed ranges of the driven device such that selection of a specific gear ratio will enable operation of the driven device within the that speed range. Accordingly, changing the desired speed and/or torque may require changing gear ratios that may be done in a step-controlled manner, i.e., gearing up or gearing down. Many operators of these machines have become accustomed to using traditional transmissions because they provide reliability and repeatability in operating the machine and, particularly, the driven device. For example, an operator may know that high gears are better suited for high-speed, low drag travel and lower gears are better suited for hauling operations or acceleration.
Recently, some manufacturers have equipped certain machines with continuously variable transmissions (CVTs) instead of the conventional, gear-based transmissions. A CVT provides an infinite or continuous range of torque-to-speed output ratios with respect to any given input from the prime mover. In other words, the output of the CVT may be increased or decreased across a continuous range in almost infinitesimally small increments. Thus, a CVT does not engage specific, discrete gear ratios to determine or control its output. However, some operators have expressed discomfort with CVTs because they lack the selectable and predicable gear ratios of conventional gear-based transmissions.
U.S. Pat. No. 7,641,588 (“the '588 patent”), assigned to the assignee of the present application, describes one approach to remedying or reducing operator discomfort and unfamiliarity with CVTs. According to the '588 patent, an electronic or computer-aided controller may be operatively associated with the CVT and/or the prime mover. The controller is configured to regulate operation of those devices within distinct output ranges provided by a plurality of discrete, predetermined speed ranges that an operator may selectively engage. The '558 patent thus provides virtual gear ratios resembling the actual gear ratios employed in conventional transmissions. The present disclosure is directed to furthering implementation and coordination of the virtual gear methodology with CVTs and to improving user operability of machines equipped with such capabilities.